1. Field of the Invention
The invention relates to a fabrication method of a semiconductor device, and more particularly, to a fabrication method of a device isolation structure.
2. Description of the Related Art
Today, development in integrated circuit fabrication is blooming. Minimization of devices is the mainstream. When the size of the device decreases, the integration of the device increases. That is, the isolation between devices must be minimized. Thus, isolation between devices becomes intractable. According to the prior art, a field oxide layer formed by local oxidation is used as the device isolation. However, edge corners of the field oxide (FOX) layer formed by local oxidation are bird's beak-shaped, and stresses may be induced. Due to bird's beak formation, it is difficult to minimize the FOX layer. Thus, it is difficult to adapt the local oxidation process to the sub-half micron process.